1. Field of the Invention
The present invention relates to a display device and a display method, and particularly to a display device and a display method by which both a virtual image corresponding to an image to be viewed by a user and a virtual image corresponding to a perception image to make the user perceive the distance to the virtual image and/or the size of the virtual image are formed to enhance the realism which is obtained by observing the virtual image.
2. Description of the Related Art
Recently, there has been implemented a virtual image viewing display device which is adapted to supply a virtual image to a user, such as a HMD (Head Mount Display).
Here, when an object is located at a position nearer to the lens than the focus distance, a virtual image is formed at the object side. The virtual-image forming principle is described in detail in "Introduction to Science of Lens (First Volume)" written by Toshio Ogura issued by Asahi Sonorama Company, "Optics" written by Kazumi Murata issued by Science Company, etc.
The adjustment condition of the convergence and focus of both eyes, the size (visual angle, angle of view) of the image (image on retina) of the object, etc. are considered as factors which make a human perceive the position of an object (the distance to the object) and the size of the object in the space.
Therefore, a virtual image visual display device may be considered as being designed to form a virtual image with realism on the basis of these factors.
That is, FIG. 1 is a top view showing the construction of the virtual image visual display device for forming a virtual image with realism on the basis of the above factors.
Each of display panels 2L and 2R comprises a liquid crystal device or the like, and images for the left eye and right eye are displayed on the respective panels. Light from the image displayed on the display panel 2L or 2R is incident to a lens 1L or 1R to be enlarged, and then incident to the left eye or right eye of a user. The display panel 2L or 2R is located nearer to the lens 1L or 1R than the focus distance of the lens 1L or 1R (at a position nearer to the lens 1L or 1R), whereby virtual images obtained by enlarging the images in the lenses 1L and 1R respectively are observed by the left eye and the right eye of the user respectively.
The virtual image visual display device shown in FIG. 1 has the lens 1L serving as an optical system for the left eye and the lens 1R serving as an optical system for the right eye. That is, it has two optical axes, and thus it is called a two-optical-axis type (device, on the other hand, a one-optical-axis type device is defined by a device in which an image displayed on one display panel is enlarged by one lens to form a virtual image, and then the virtual image is observed by one eye or both eyes.
In the two-optical-axis type of virtual image visual display device, the distance from a user at which the virtual image is observed by the left eye or right eye of the user (the position at which the virtual image is formed) (virtual image imaging position) can be varied on the basis of the positional relationship between the lens 1L and the display panel 2L and the positional relationship between the lens 1R and the display panel 2R.
Accordingly, the adjustment condition of the convergence and focus of both eyes can be varied by adjusting the positional relationship between the lens 1L and the display panel 2L and the positional relationship between the lens R and the display pane 2R, thereby allowing the use to perceive the position of the virtual image (the distance from the user to the virtual image).
Further, as shown in FIG. 2, when the size of the retina image is fixed, the user perceives that the virtual image is larger as the distance to the virtual image becomes longer. Accordingly, the size of the virtual image which is perceived by the user can be varied by adjusting the positional relationship as described above to vary the position at which the virtual image is formed. Conversely, when the distance to the virtual image is fixed, the size of the virtual image which is perceived by the user can be varied by varying the size of the retina image.
As one type of virtual image visual display devices has been known a see-through type in which incidence of external light is allowed. In this case, the user can observe not only the virtual image (virtual image frame and virtual image space), but also the outside scene outside condition and real space). Therefore, there is a case where no virtual image with realism is obtained in accordance with the environment of the real space.
That is, the position and size of an object in the space which are perceived by the human is greatly affected by not only the convergence and focus adjustment condition of both the eyes and the size of the retina image, but also the effect based on visual psychology. That is, in the case where the virtual image space can be seen together with the real space, the psychological effect which is obtained by comparing an object existing in the real space and its virtual image has a great effect on the position and the size of the virtual image which is perceived by the user.
Specifically, for example, as shown in FIG. 3, when an object (obstacle) existing in the real space is located between the user and the virtual image, the user may originally see the overall obstacle as shown in FIG. 4A because the obstacle is located in front of the virtual image.
However, in the virtual image visual display device shown in FIG. 1, the visual field is intercepted by the images created with the display panels 2L and 2R, so that the obstacle located in the intercepted range is not seen as shown in FIG. 4B.
As described above, there occurs such a phenomenon that the obstacle located in front of the virtual image is hidden behind the virtual image and thus it cannot be seen, which is impossible in the real space. Accordingly, the position and size of the virtual image cannot be accurately perceived due to the above inconsistency, so that the virtual image with realism may not be obtained.
Therefore, there is a method of intercepting the outside light to the virtual image visual display device to prevent the user from seeing the external scene (real space). However, since the external light is intercepted to avoid use of the psychological effect which greatly affects the position and size of the object perceived by the human, that is, the object which is to be compared with the virtual image is hidden, the position and size of the virtual image is not accurately perceived, so that no virtual image with realism is obtained.